Tailpipe or afterburning control for turbojet engines



Dec. 18, 1956 F. c. MOCK ETAL 2,774,215

TAILPIPE OR AFTERBURNING CONTROL FOR TURBOJET ENGINES Filed April 22, 1949 4 Sheets-Sheet 1 AFTEFBl/RA/IA/ FHA-2 M5756! THE an 051' ATIC IVIGIVEWC 6207C yap/2r INVEN TOR. PAW/VA c. Mad/K 57/0/74; .1 Maw/w ATTO/VA Z') Dec. 18, 1956 F. c. MOCK ETAL. 2,774,215

TAILPIPE 0R AFTERBURNING CONTROL FOR TURBOJET ENGINES Filed April 22, 1949 4 Sheets-Sheet 2 FRANK #555??? game: J flew/P50 Dec. 18, 1956 c, MOCK ETAL 2,774,215

TAILPIPE 0R AFTERBURNING CONTROL FOR TURBCIJET ENGINES Filed April 22. 1949 4 Sheets-Sheet 5 I V N TOR.

Flaw/A a 7/50? I rev/m: .xr/m/mmv ATTORNEY Dec. 18, 1956 c, oc ETAL 2,774,215

TAILPIPE OR AFTERBURNING CONTROL FOR TURBOJET ENGINES Filed April 22, 1949 4 Sheets-Sheet 4 luv: R T a; :E /64 VAR lAaLe.

M7 RESIST- TENTlOMETER /50' Mow-oh TIEA B W M ATTOFA/E) TAILPIPE R AFTERBURNING CQNTROL FOR,

TURBOJET ENGINES Frank (3. Mock and Thomas J. Thompson, South Bend,

Ind., assignors' to Bendix Aviation Corporation, South Bend, Ind., a-corporatiou of Delaware Application April 22, 1949, Serial No. 89,054

35 Claims. (Cl. 60-f3fi6) This invention relates to turbojet engines for aircraft, and is particularly concerned with means for. obtaining thrust augmentation in such engines by burning fuel in the tailpipe or tail cone section thereof.

The instant application incorporates, but. does not.

claim, certain subject matter common to the following copending U. S. applications (common assignee): Serial No. 25,828, Mock, filed May 8, 1948, now Patent No. 2,736,166, issued February 28, l956g'Serial No. 30,828, Thompson, filed June 3, 1948; Serial No. 82,792, Kuz-' mitz filed March 22, 1949. i

This method of obtaining thrust augmentation is commonly termed tailpipe burning or afterburning. In the following description, the latter term will bemore frequently used for the simple reason that it is the shorter of the two, although perhaps less apt.

When burning fuel in the tailpipe area after the tur blue, it is important to maintain a balanced condition between the turbine and compressor, and this in turn calls for coordinated regulation of the rate'of fuel feed and exhaust jet nozzle area. In Serial No. 25,828, the two principal factors to be controlled, viz. jet nozzle area and the rate of fuel feed, are coordinated by interconnecting the gate valves which control the exhaust jet nozzle and the afterburning fuel metering means through a suitable corrective device which responds to a preselected ratio of tailpipe and ram or compressor inlet pressure in one instance and temperature in 'the other. In Serial No. 30,828, the means for maintaining a prescheduled rate of fuel feed and jet nozzle area includes a device which operates as a function of engine speed. In Serial No. 82,792, the rate of supply of the afterburning fuel is a function of compressor discharge pressure and jet nozzle area. In the latter application, also, when the pilot sets his control lever for afterburning, such will not talge place unless the aircraft is traveling below a predetermined rate of speed, nor can the gate valves open and full afterburning'be had until a certain amount of starting fuel has been burnedin the tailpipe chamber.

n In the present application, compressor discharge (Po) pressure is also used as a metering modulus, and here again jet nozzle area and the rate of fuel feed is coordi nated, but coordination is had across the throttle valve and interrelated regulator system of an afterburning fuel metering device and is subject to modification by means responsive to tailpipe temperature. When the pilot sets his control for afterburning, the latter will not occur unless or until a certain predetermined engine speed is attained, whereupon starting fuel is first supplied to'the tailpipe chamber and ignited, and when the temperature in said chamber rises to a certain value, the area of the'ex haust jet is increased and simultaneously therewith afterburning fuel is metered to all of the afterbu'rning nozzles and ignited for normal or full afterburning operation, during which the rate of fuel feed is governed as a fund tion of P0 pressure subject to correction by means operating as a function of tailpipe temperature nhumane latter constant.

2,774,215 Patented Dec. 18, 1956 An objectof the presentinvention, therefore, is to sim plify and generally improve afterburning systems for:

turb ojetv engines.

A more specific object is to provide improvements in the means for coordinating the fuel metering rate and.

exhaust jet nozzle area to obtain maximum overallengine efficiency.

Another object is to provide metering means for the,

afterburning fuelwhich operatesautomatically as a func: tionof compressor discharge pressure and/or tempera ture and which is subject to correction. by means responsive to tailpipe temperature to maintain the latter at some predetermined value.

A further object is toprovide automatically operating afterburning devices responsive to engine speed and tail-f pipe temperature to insure against overspeeding of the en gine should the starting fuel fail to burn or in; case of lack of. afterburning fuel or failure ofthe fuel: supply.

Other objects and advantages willbecome apparent in View of the following description taken in conjunctiorr with the drawings, wherein:

Figure 1 is a schematic view of a turbojet engine.

equipped. With an afterburning. system in accordance with.

ture correcting and amplifier unit which may be used for modifying the rate of fuel feed to obtain a constant or predetermined tailpipe temperature; and

Figure 4 is a schematic sectional view of a modification in the afterburning fuel'control device of Figures 1 and 2:

The turbojet engine shown more or less diagrammatically in Figure 1 and generally indicated at 10 includesa burner system made up of a plurality of annularlyarranged combustion chambers 11, each having therein a flame tube" 12, the walls ofwhich are formed with a series: of openings 13 for admitting air thereinto from its sur=' rounding chamber 11. An air adapter or header section 14 is detachably connected to the front end of the burner assembly anddirects air under pressure to the chambers 11, where part of the air enters the flame tubes 12 through the holes 13 and mixes with the fuel discharged from burner nozzles 15, there being one for each flame tube. The gases comprised of expanded air andproductsof combustion aredischarged from the flame tubes through stator blades 16 and turbine blades 17, the latter forming part of a turbine rotor 17. A dynamic compressor is generally indicated at 13; it is shown asbeing of these];- trifugal type, but may, of course, be of'the axial flow type; it is driven from theturbine and is shown mounted on a shaft 19 common to'the turbine rotor and com pressor.

Beyond the turbine is the tailpipe 21); it carries a diffuser cone 21 at its entrance end and at its outlet termi hates in a reaction jetor nozzle 22,the area of which is adjustable by means" of a pair of gate valves 23 and 24 mounted on suitable bearings such as' trunnion's'or short shafts 25 and 26. Also" secured onsaid shafts are intermeshing segmental gears 27 and 28. .An arm 29 is secured at one end on the shaft 25 and at its opposite end is connected through the medium of a link rod 30 with a serv'opiston 31s lidably mounted in a cylinder 32. The piston 31 is preferably operated by compressor discharge or P0 pressure in amanner to be described.

Any suitable typeof main fuel supply system maybe adopted, that'shown in the present instance and generally designated at 33 in Figures 1 and 1A isof'the type illust'ra'tedin acopendingapplica'tion of Frank C. Mock,

Serial No. 716,154, filed December 13, 1946, now patent No. 2,689,606, issued September 21, 1954, and assigned to the assignee of the present application. Fuel is supplied under pressure from a suitable source of supply such as a fuel tank, not shown, by way of conduits 34, 34' in which is mounted an engine-driven fuel pump 35 of the positive displacement type having a by-pass 36 controlled by a suitable by-pass valve, not shown, but which is adapted to maintain the supply pressure at a predetermined value over and above metered fuel or discharge pressure. The device indicated at 37 is a bellows housing which forms part of a density control system for regulating the rate of fuel feed to the burners 12 as a function of changes in pressure and temperature of the air-flowing to the engine. The metered fuel from the main fuel control 33 flows by way of a conduit 38 to a fuel manifold 39, from which it flows to the respective garner nozzles 15 through a series of branch nozzle pipes An emergency fuel metering system is usually provided. In the present instance it is shown in block diagram at 41 and may be in the form of an engine driven fuel pump located in an extension 42 of the conduit 34', the fuel being by-passed around the main fuel control 33 byway of a conduit 43 and thence through a double check valve 44 into the conduit 38. The emergency system is primarily for use in case the main fuel control should fail or become ineffective and may be controlled by the pilotin any suitable manner, not shown.

The rate of fuel feed is under selective control from 3 the pilots compartment by means of a suitable power lever 45 adjustable along a quadrant 46, said lever being pivoted at 47 and connected by suitable linkage 48 to the governor or throttle valve of the main fuel control. Purely by way of example, the quadrant has indicated thereon four control positions, viz. fuel cut-off, at which position all fuel flow to the burners is stopped and the engine is closed down; idle, at which position the engine is operating at a suitable idling speed; maximum power, at which setting the engine is delivering at some predetermined maximum power output on the main fuel control; and augmented power, at which position the after burning system is placed in condition for operation automatically in a manner to be described.

The lever 45 is provided with a lateral projection 50 movable in a slot 51 formed in the quadrant 46; and when the said lever is set at augmented power, the projection 50 moves into a communicating offset slot 52 and depresses a switch plunger 53, forming part of a main control switch, generally indicated at 54 and including a pair of contacts 55 and 56 adapted to be bridged by a conductor 57 when the plunger 53 is depressed. This energizes a circuit leading by way of wires 58, 59 and 60 from a suitable source of electric power, indicated as a battery 61, to a speed-sensitive switch, generally indicated at 62, adapted to respond to changes in engine speed. In the form shown, the switch 62 is responsive to the differential between unmetered fuel pres sure in the regulator chamber of the main fuel control and unmetered fuel pressure in the governor chamber in the immediate area of the rotating governor weigh-ts and which pressures vary with variations in engine speed but are unaffected by changes in air density or altitude.

' A differential exists between these respective pressures (commonly termed P2 and P's pressures) due to the fact that the governor chamber pressure is augmented or amplified by the centrifugal action of the rotating governor weights, one of which is visible in the said governor chamber. Said switch 62 has a pair of contacts 63 and 64 adapted to be bridged by a conductor 65, carried by a diaphragm 66, which constitutes a movable wall between chambers 67 and 67'. F2 pressure is communicated to the chamber 67 by a conduit 68, and P2 pressure is communicated to the chamber 67' by a conduit68'. A light spring 69 normally urges the diaphragm toward a non-contacting position.

When the speed responsive switch 62 is closed, the solenoid coil 71 of a magnetic clutch 72 is energized by way of line wires 73 and 74. This action starts operation of a constant displacement engine-driven pump 75 which takes fuel'from the main fuel line 34 by way of conduit 76 and pressurizes it by way of conduit 77 to the intake chamber 78 of an afterourning fuel control unit generally indicated at 79 and shown more or less in detail in Fig. 2. Should the fuel in the chamber 78 exceed a predetermined pressure, it opens a bypass valve 31 and fuel may then pass back to the low pressure side of the pump 75 by way of port 81', chamber 82 and return conduit 83. The by-pass valve 81 is connected to a diaphragm 84, which forms a movable wall between the chamber 78 and a chamber 85 in which a spring 86 is mounted and normally urges the valve 81 towards seated position. The chamber 85 is preferably vented to metered fuel or discharge pressure by way of passage 87 having a suitable restriction 87" therein, and passage 87, so that the valve 81 (which is of the balanced type) will maintain the pressure in the chamber 78 at a predetermined value over and above metered fuel pressure as determined by the strength of the spring 86. A normally closed spring loaded relief 80 is mounted inside valve 81, and is adapted to open a port in the end wall of valve 81 for relieving the pressure in chamber 78 in the event it exceeds a predetermined maximum value.

A regulator valve is indicated at 88; it is of hollow cylindrical form and provided with ports 89 adapted to register with ports 90 formed in a similarly-shaped coacting valve 91 which is slidingly telescoped into the valve 88. The valve 88 is controlled as a function of tailpipe temperature in a manner to be described, while the coacting valve 91 is controlled as a function of jet nozzle area, also in a manner to be described. Fuel from chamber 78 flows into annular valve chamber 92 and thence across ports 89, 90 and 90 into chamber 93. From this chamber, fuel flows across a metering valve 94, which is provided with ports 95 and is mounted to slide in a cylindrical valve casing 96 provided with ports 97, the ports 95 and 97 coacting to provide a variable metering restriction. The valve 94 is connected to and actuated in response to movement of a capsule or bellows 98 provided with a connecting stem 99, said bellows being mounted in a chamber 100 to which compressor discharge or Po pressure is communicated by way of conduits 101 and 102. A calibrated drain bleed 103 vents the chamber 100 to the atmosphere or other suitable low pressure source.

Reverting now to the regulator valve 91, it is connected to a diaphragm 104, which forms a movable wall between the chamber 93 and a chamber 105, vented to metered fuel or discharge pressure by way of a passage 106 having a calibrated bleed or restriction 107 therein. The chamber is also preferably vented to the chamber 93 across diaphragm 104 by a passage 109 having a calibrated restriction 108 therein. A spring 109 ongages the diaphragm 104; its effective force is adapted to be varied or adjusted by means of a cam 110 mounted on a shaft 111; and the tail gate servomotor piston 31 is operatively connected to the said cam shaft by means of a rod 112, bell crank lever arms 113, 113', link rod 114 and arm 115, the said bell crank being pivotally anchored at 116, compare Figs. 1 and 2.

The fuel metering rate across the regulator 79 will vary as a function of (a) Po or compressor discharge pressure through variation of the metering restrictions or ports 95, 97 in response to movement of the bellows or capsule 98; (b) exhaust nozzle area through variation of the metering head by rotation of cam 110 in relation to movement of the tail gate valves 23 and 24 and consequent repositioning of valve 91, and (c) tailpipe temperature also through variation of the metering head by repositioning of valve 88 due to the action of the temperature responsive device of Fig. 3 to be described. At any given position of valves 94, 88 and 91, the regulator will be in balance and the head across valve;94 will be constant; and if atysuch -timor the area? of the meteringprestrictions 95,: 97 be. increased,

therewill bean increasefiniflow across said restrictions and also a momentary reduction in the differential across;

of fuel flow. The vent passage 108 is provided primarily; to assist in the removal of any vapors; that. may. tend to forrn in theregulator and thereby unbalance the latter,

Fuel flowing across the valve94 enters meteredfuel chamber 117 and passesfrom this chamber through conduit 1 18, port 119 and'conduit 120, firstto the starting system, and after ignition and burning of the. starting fuel, to the main afterburning fuel manifold and discharge nozzles:

Referring to the startingsystem, this may comprise one or more starting torches or nozzles, one of which is'indicated at 1'2'1, receivingfuel from theconduit 120 by way of starting fuel manifold 122 and pipe 123. Starting fuel may alsoflow by way of pipe or conduit 124 to any selected one or more of the mainfuel discharge nozzles, two of which are shown at 125, the latter receiving fuel from a'main afterburning fuel manifold 126 and pipes 127. A spark plug or other suitable ignition device is indicated at128"; it is energized, when the speed responsive switch.

62' is closed, by way of line Wires 73,- 74 and 129. To prevent how of starting fuel into the manifold 126 and premature firing of the afterburning system, a check valve 130 is provided betweenthe said manifold and any of the conduits 124 which supplyfuel' to the starting. nozzle or nozzles. A starting cut-oft valve is indicated at 131;.

it is of the normally closed electric type and. has a solenoid coil 132 which is energized when the temperature in the tailpipe attains a certain predetermined value and opens the" said valveto permit fuel to How to all of the after-burning" nozzles 125. Accordingly, a thermostatic switch, generally indicated at 133, islocate'd in. the tailp pe adjacent the exhaust jet nozzle 22; it includes a pair of contacts 134 and 135 carried by a pair of bimetallic elements 136, 136'. When speed responsive switch 62 1sclosed current may flow by way of line wires 73 and 137 to the switch" 133, and if the latter is' also closed, then current will flow thereacross and by way of wire 137 to theeoii 132 of the starting solenoid valve 131.

The tail gate control servopiston 31 is preferably actuated by compressor discharge pressure which is controlled by means of an electric servo comprising a valve 138 mounted to slide in a valve body 139. The valve 138 is normally urged toward closed position, or toward the left as shown, by a spring 140. The valve body 139 has an inlet port 141, a pair of outlet ports 142 and 143, and a pair of drain or air relief ports 144 and common drainpipe or conduit 146'. A solenoid coil 147, serves to actuate the valve 138 to the right, as shown, aga nst the compressive resistance of the spring140, the said coil being energized, when the switch 133is closed, byway of line wires 137 and 148. A conduit 149 com: mhnicates port 142 with the servomotor cylinder 31 on the left-hand side of piston 31, and another conduit 150 communicates port 14-3 with said cylinder on ther'ight hand side of said piston.

hi the position of the servo valve 138 as shown, Pcor compressor discharge pressure is being communicated to the left-hand side of piston 31 by way of conduit 1 01, ports 141, 142 and conduit 1 49, holding the said piston in a gate-valve-closing position. At this time, the temperature switch 133 is open and the solenoid coil 147 is tie-energized, Under these conditions, the engine is opg. on the normal fuel supplied by the main fuel con; trol Should temperature switch 133 close," coil 1'47 145 opening to a wpuld. become. energized and. servo valve 13s,, wo mov to tlierightjand communica per" 142,,with 144, whereupon P pi'essu w 111' be C cated byway of conduit totheservornoto connected by wires 154 and 59 with contact 56 of the pilotscontrol switch 54. When the-pilotlsets hislevet' for afterburn-ing, be automatically opens valvejI5 2. This I valve avoids leakage: and consequent loss ofpress'uji 'e when the afterburning system is not being'used. H

The port 119 between the fuel conduits 118 and 12!} is controlled by a valve 155, which is of the normally closed solenoid type and is opened through energization'of coil 156, connected by line Wires 157, and 73 with thefcontact 64 of the speed sensitive switch 62, Thus, when switch 62 closes, valve 155 opens, and" when switch 62 opens, valve'155 closes.

The means for repositioning the valve 88 of the fuel metering device 79 as a function of tajilpipe temperature may be of any suitable type. In the example chosen for the purposes of illustration,- it comprises an induction motor having, a control circuit shown in block diagram, at 161 in Figure l and more indetail in the elec' trical diagram of Figure 3. The motor has a stator winding of-the two-phase A. C. reversing type comprising a fixed phase field coil 162 and a variable phase coil 163. An alternating current potential may be had by means of a suitable inverter 164 having its input connected to a source ofv direct current potential, not shown, or the A. C. supply may be' taken from a generator orother convenient source. The rotor 165. :of the motor is co nnected to the valve 88' by means of an arm 166; linlt 1 67, arm 168, shaft 169, and slotted armf170, th'e latter having a slot and pin connection with the" stern of said valve (compare Figures 1 and 2). The means for sensing tailpipe temperature includes a thermocouple 1 71 which is electrically connected to a bridge circuit 172. The voltage impressed on the fixed phase coil or winding 162 is shifted nearly ninety electrical degrees with respect to the supply voltage by a series'cap'acitor 173; The voltage impressed on the winding 162 is supplied through a saturable reactor 174; it is so designed that if tubes 175 and 176 are conducting the same average current, the voltage applied to the variable phase winding 163 will be zero and the motor will not run, but if onetube is conducting a plate current of greater magnitudeth an the other, a voltage will be applied to the winding 163 and the motor will run in one direction, the motor reversing when the current is of greater magnitude in the opposite tube. V V

The function of the bridge 172 and associated motor control circuit is to take a signal from the thermocouple 171 when the latter senses temperatures above and/0r below a calibrated value and cause the motor arm 166- to make a partial turn in one of two. opposite directions; and position the valve 88 of the fuel control device 79 of Figure 1 in a manner such as to maintain the tailpipe temperature substantially constant. Also, when the afterburning system is turned off or is not being used, to cause the said valve to come to rest" at a position corresponding to some predetermined tailpipe temperature, and which may be the calibration temperature at which the bridge 172 is balanced, so that when the after burning system is again turned on, said valve will be already set at a position for establishing the desired temperattire.v Accordingly, the bias battery indicated at 177 is of suchmagnitude and direction as to cause tube shut-ofi-wh ei no current is flowing in the secondary 17-8' of transformer 179. However, when the A. C. grid voltage of either tube .175 or 176 is in phase with the plate voltage between the points indicated at x, y, the tube will conduct. The phase-splitting transformer 179 supplies voltages to the grid circuits of tubes 175 and 176 which are 180 electrical degrees out of phase with one another. The primary '178 of transformer 179 is connected into the output circuit of an amplifier 181, which may be of the conventional audio type employing feed-back for stability purposes and is not shown in detail. The input circuit to the amplifier is connected across the secondary 182' of a transformer 183, the primary 182 of said transformer being connected across the signal circuit 184 of the bridge 172. The device indicated at 185 is a variable resistance or socalled acustilator comprising a container or box of carbon granules with a diaphragm 185 overlying the same which vibrates in response to changes in the magnetic field of coil 186; it functions to change the D. C. current flow from the bridge circuit to a pulsating current at a frequency determined by that of the power transformer 187. The direct current voltage impressed on the acustilator 185 and the primary 182 of transformer 183 is of a magnitude proportional to the degree of unbalance of the bridge 172 and of a polarity dependent on the direction of unbalance. In other words, the magnitude is proportional to the rise in tailpipe temperature above or the drop below a predetermined value, and the polarity changes each time the temperature goes above or below such value. Further, the periodic variations in resistance across the acustilator 185 produces a voltage output from the secondary 182' of transformer 183 of a magnitude proportional to the direct current voltage impressed on the acustilator and the primary 182 of said transformer, and a phase relationship with respect to the voltage between points x and y dependent upon the polarity of the applied direct current voltage.

A relay switch is indicated at 188; it is designed to connect the bridge circuit with the thermocouple 171 by engaging contact 189 when the afterburning system is in operation and to connect said circuit with the wiper :arm 191 of a potentiometer 192 by engaging contact 190 when the said system is turned off. The switch 188 is held in engagement with contact 189 through energization of solenoid coil 193, which is electrically connected to contact 64 of the speed sensitive switch 62 of Figure l by means of wires 194, 157 and 73. The motor 160 has a follow-up connection with the wiper arm 191 by means of suitable mechanical linkage indicated at 196 in Figure 3.

The bridge circuit may be energized from a source of regulated direct current voltage shown in the form of a tube rectifier 197 having its input inductively coupled with the main supply through transformer 187 and its output connected through a voltage regulator tube 198 with the bridge input, the said tube 198 maintaining the voltage applied to the bridge circuit within close tolerances.

If at the time the afterburning system is turned off the motor should stop at some position at variance from the balanced setting of the bridge, the wiper arm 191 will be off-center and will unbalance the bridge in a direction such that the signal output of the transformer 183 will have a phase relationship to the motor winding 162 tending to rotate the motor in a direction to reduce the error, until the bridge output becomes zero at what may be termed a false signal having as its modulus some predetermined tailpipe temperature.

When the afterburning system is turned on and the speed sensitive switch 62 closes, relay coil 193 will be energized and move switch 188 into engagement with contact 189. This connects the thermocouple with the bridge circuit, and if at this time the temperature sensed by the thermocouple does not correspond to the calibration of-the bridge, then the latter will become unbalanced in a direction such that the signal output of the transformer 179 will have a phase relationship to motor wind ing 162 such as to produce rotation of the motor in a' direction to position valve 88 for correction by regula tion of fuel flow.

Operation tion of the control lever shown in Figure l, the engine would be closed down and all flow of fuel to the burners cut 011. Between cut-off position and up to and including the maximum power setting, the engine operates solely on the main burner system.

The various parts of the afterburning system are shown in a non-operating position, the master switch 54, which responds to the pilots control lever 45, being open. Accordingly, the Po solenoid valve 152 and the cut-off valve 155 are both closed; the speed sensitive switch 62 is deenergized as is also the safety starting temperature responsive switch 133; the switch 188 of the temperature responsive motor control unit of Figure 3 will be in a constant temperature false signal position (in engagement with contact 190); the magnetic clutch 72 of the fuel pump 75 will be released, and the spring 140 of the electric tail gate servo valve 138 will be holding the valve in the position shown, at which time the tail gates 23 and 24 are closed to a point where the area of the jet nozzle 22 is such as will give maximum thrust under normal engine operating conditions.

Assuming the pilot is operating at a maximum power setting and decides to utilize the added thrust available by afterburning, he then moves the lever to the augmented power position and simultaneously closes the switch 54, whereup the Po valve 152 is opened, and the speed sensitive switch 62 is energized. If we now as sume that the speed of the engine is within a predetermined range tending toward maximum efficiency under afterburning operating conditions, the speed sensitive switch 62 will close, whereupon (a) current will flow to the solenoid coil 156 of the cut-off valve 155 which controls the port 119 and opens said valve, (b) current will flow to the hot side of the temperature responsive safety starting switch 133; (c) the ignition system of spark plug 128 will become active; (d) the switch 188 of the temperature responsive motor control unit of Figure 3 will be moved from its constant temperature false signal position to actual tailpipe temperature sensing position (in engagement with contact 189), (e) the magnetic clutch 72 will close and start the pump 75 in opera-' tion so that it delivers fuel to the entrance chamber 78 of the fuel metering device 79, from which it flows across the regulator valves 88, 91 and metering valve 94 and thence by way of conduit 118, port 119 and conduit 120 to the starting fuel manifold 122 and starting torch 121. The starting fuel flow now ignites and proceeds to burn in the tailpipe chamber and raise the temperature therein.

When the tailpipe temperature rises to a value such as will cause the safety starting switch 133 to close, (f) the solenoid coil 147 of the electric servo valve 138 will be energized and the valve 138 will be moved to'the right from the position shown and cause the servomotor piston 31 to move to the left and open the tail gate valves 23 and 24, and (g) the solenoid coil 132 of the normally closed fuel cut-off valve 131 will be energized and said valve will open, permitting fuel to flow to all of the' afterburning nozzles 125.

As the tail gate valves open, the cam is rotated in a counterclockwise direction, compressing spring 109 and opening the regulator valve 91 to increase the meter: ing head across the valve 94. This provides a scheduled relationship between jet nozzle area and afterburning fuel flow, as required by the engine during the transh tion from normal to augmented thrust conditions.

The foregoing series of stepsbring the afterburnifig system into full operation it will be noted that the jet nozzle area will remainflnormal until, after a sure indication is had that the tailpipe temperature had been increased by burning of the afterburning startingfuel. .11? at any time during the starting period there is areduction in engine speed due for example to die-out in the normal burner system, the speed sensitive switch 62 will immediately open and prevent operation of the afterburning system. Furthermore, in case the afterburning system should fail, there would be a drop in temperature in the tailpipe chamber and switch 133 would open, shutting down the afterburning system: and preventing loss of fuel and possible serious overspeedin'g of the engine.

During normal or full afterburning operation; the metering device 79 operates automatically to meter a'fterburning fuel as a function of compressor discharge pressure. The metering restrictions 95 are calibrated to provide as nearly as possible the correct scheduledfuel flow for efficient afterburning, any error being shb ject to correction by the action of the taiIpipeitemPera ture corrector. The corrective action of the P6 orcom pressor discharge responsive bellows or capsule 98 tends to increase the metering rate of the afterburning' fuel as the engine speed increases, and to'decrea's'e sues rate as the engine speed decreases, whereas: the corrective action of the tailpipe temperature regulator tends to iiicrease fuel flow as the tailpipe temperature drops and to decrease fuel flow as the tailpipe temperature rises. Thus, as the engine speed increases andPc' pressure rises, the bellows 98 is compressed andthe area of the meter-' ing restrictions 94, 95'1'ncreases; and as. the tailpipe ten-i perature rises, the regulator valve 88 moves" to theleft and reduces the metering head across the valve 94', and as the temperature in-the tailpipe drops, the said" valve 88 moves to the right and increases the meter'inghe'ad across the said valve 94. By correlating the metering aiaractene tics of the valve 94 with those of the valve 88, a stableoperation of the afterburning' system is obtained- Whenthe pilot moveshis control lever out otf'tlie iiifg mentedpower position, the master switch 54 operas, thereby cutting off current to the speed responsive switch 62 and the coil 153 of the Po solenoid valve 152. Also,- the controls which normally respond to the speed 'switch 62 are d e-energized, viz. the magnetic clutclisolenoid coil 71, the safety starting switch 13-3, and the relay coil 193 of theswitch 188; whereupon thepump 72 idles, the electric servo valve moves-back to the position shown, causing the gate valves 23' anti2'4 to close to" normal thrust area, the temperature responsive motor control circuit is reset to'constant'temperature falseart; erburniug signal, the fuel cut-oil valves I'I9f'and 1 31 close, shuttingoif all flow of fuel to the afterbtirniiig nozzles including the startin'g nozzles, and tli'e' spark pliig' 128 is de-energizedl Figure 4 In Figure 4-, an afterburningf. fuel" cont'rol's'ysteni shown which operates in a manner" different neat are fuel control of Figures 1 and 2 although" the ultimate result is substantially the sam'ei The manners the supply pump enters the unit by way of conduit-77, a-ndflowsiacross a regulat vane 200 which is slidably mounted in a" ported sleve as bushing-2411, thesleeve and" valve beirigi'provi'deifv'vitlt coacting ports 2G2 through'which the fuel 'flowsto elf her 203. The valve 200'is conriectedft'o' a dia'ph grit" 204,v which forms a movable wall betweeiiich'ambers 205 and12tl6, said diaphragm being ba'cleedbya spring flfi' of substantially constant rate and-which mamas-adjusted by rneans of "screw 2%." p p The valve. indicatedlat 209-is a threats-w sponds to the valve-:94 of Figuresl and? toslideFin a sleeve or? bushing21'0; said" undensupply ump-" ressure 1 beirig' provided witlr coactihg- .fe'ed restrictionsaor ports 211i The fuel flowing across the valve 209' enters-me teredlftiel chamber 212, from which it' fiowsflby way of conduit 1*18" to the afterburningtstarting and main fuel discharge nozzles 121 and 125 of Figure l.

The valve 209 is operatively connected to the tail gate valves and 24 of Figure lby means of a link rod 112', bell crank levers 213', 214 and valve stem or rod 215: Thus, as the tail gate valves open and close a proportional movement will be imparted to the throttle valve 209, and at any given metering head across the throttle valve, fuelflow will be proportional to jet nozzle area. In the type of fuel control shown in Figure 4, instead of adjusting the throttle valve directly as a function'of PE or compressor discharge pressure, the metering head across the valve is varied as a function ofcompressor discharge pressure and a temperature varying as a function of engine or compressor inlet temperature subject to correction by deviation of turbine outletor tailpipe temperature from a predetermined value. To accomplish this result, a fixed bleed 2116 communicateschambers 205" and 206 across the diaphragm 204, and

fuel in chamber 206 may bypass the throttle valve 209 by" Way or passa e 217', variable orifice 21s, chamber 219; and'passa-ge 220. The variable orifice 218 is in series with the fixed bleed or orifice 216; it is controlled by a" censured needle 221 which at its outer end has a swivel or pivotal connection with a crank-shaped lever 222, secured on the lower end of a shaft 223, which projects upwardly through a sealed bearing in' the housing of theuiriit into" a chamber 224 and is adapted to be reversely rotated in respohsc to movement of a bellows- 225 aridal's'd by motor which corresponds to the meter 168 of Figures 1 and 4 and is driven in reverse directions in response to signals from the temperature sensitive unit 161. Accordingly, the bellows 225 is provided with a rack; gear 225 at'its free or movable end which is constantly in mesh with a gear 227 formed on the lower endof a hub 227, the latter being mounted for free rotation on shaft 223" andat its opposite end having formed thereon another gear 228 constantly in mesh with one of a pair of planetary pinions 22 9 and 229', the latter being carried by a stub shaft 230' journa'led in the peripheral portion of a drive plate 230, u'lhich is scented to" and drives the shaft 223.

The motor 160' hasa' drive pinion 231 secured on the free end of its armature shaft which is in constant mesh with a gear 232, formed on the upper end of a hub 232, the lat'teilile" the hub 22 7 being mounted for free rotatioi'i on shaft 2235 The lower or opposite end of the hub 232" has formed thereon a gear 233 in constant mesh with pinion 229 a If" gear 227" is rotated clockwise, for instance, gear 228 woul'dalsd be rotated in the same direction and rotate pinions 229and 229 in a counterclockwise or opposide' direction'; If at this time gear 233 is held against rotation; then the pinion 229 will walk around the latter gear counter-clockwise and produce like rotation of the ante plate 230i Conversely, if gear 233 is rotated clockwise, pinioris 229; 229' will rotate counter-clockwise; and if at" this time gear 227 is held against rotation, piiiion 229Iw'ill walk around the gear 228 and produce lik remiss of drive plate 230. Hence shaft 223 may bedriven by'mbvement of rack 226 or rotation of the otof drive gear 231, the drive of one being independent of the'otlrer. The differential mechanism shown in Fign'r'ej 4 is simply for illustrative purposes only, it being uiiderstood that in practice any type of differential unit suitablefor'the purpose may be used.

The bellows 225 is mounted in a chamber 234,.a'nd regulated Pd or compressor discharge pressure is conimiiriifc atedto this-chamber way of conduit 235, chain, has 236, vs'riabls onnce 237, "chamber'2i38 ana cond t" csmprasser assua e temperature; its" area is sentence by a needle 240 secured to the free or movable end of a stack of by-metallic disks 241, which are located in chamber 236. These disks have the characteristic of contracting upon an increase in temperature and expanding upon a decrease in temperature. Thus an increase in compressor discharge temperature will move needle 240 in a direction to restrict orifice 237, a decrease in such temperature having the opposite effect. Obviously, the desired efiect could be obtained by a temperature responsive unit working in the opposite direction with a reversely contoured needle. The wall of the bellows chamber 234 is provided with a bleed 237 in series with the variable orifice 237.

Assuming there is an increase in P or compressor discharge pressure at a given area of orifice 237 (constant temperature), the bellows 225 will collapse and produce rotation of the shaft 223 and crank arm 222 in a clockwise direction, thereby moving the needle 221 in a .direction to restrict the orifice 218, an expansion movement of said bellows having a reverse effect. Should there be a change in compressor discharge temperature, the area of orifice 237 will be correspondingly varied, thereby modifying the effective force exerted on the bellows by the then existing compressor discharge pressure. The action of the bellows 225 thus becomes a functionof changes in both pressure and temperature. Also, the shaft 223 may be rotated by the motor 160' in either direction, depending upon whether there is an increase or decrease in temperature in the tailpipe above or below some predetermined value, heretofore described. If there is an increase in temperature, the motor 160' will produce rotation of shaft 223 in a direction which will move the needle 221 outwardly and increase the area of the orifice 218; a drop in temperature having the opposite or reverse effect.

While the temperature sensing device 241 is shown as being subjected to compressor discharge temperature, it could also be subjected to compressor inlet temperature, since compressor discharge temperature at a given engine speed is a function of compressor inlet temperature.

In Figure 4, the potentiometer which corresponds to 192 of Figure 3 is indicated at 242; it has a followup mechanical connection with the motor 160' by means.

of gears 243 and 244, and suitable electrical connections with the switch contact 190 and the bridge circuit at 245.

Operati0nFigure 4 The spring rate of the spring 207 is preferably substantially constant, so that the force exerted by said spring may be considered as remaining constant and the respective pressures in chambers 205 and 206 will tend to bear a constant relative value. Thus, the valve 200 will open or close to maintain the pressure in chamber 2195, and hence in 203 equivalent to that in 206, plus the force exerted by spring 207. Hence, a substantially constant differential will be maintained across the diaphragm 204, varying only momentarily as the pressure in either of said chambers is varied. The chambers 205 and 212 are connected by two passages in parallel, one comprising the chamber or elongated passage 203 and feed restrictions 211, and the other the fixed bleed 216, chamber 266, passage 217, variable orifice 218, chamber 219 and passage 220. With this arrangement, the drop in pressure from chamber 205 to chamber 212 across the throttle valve ports or feed restrictions 211 will always equal the sum of the drop in pressure from chamber 2% across the fixed bleed or orifice 216, the passage 217, variable orifice 218, and passage 220. The substantially constant drop across the fixed orifice 216 as determined by the spring 207 creates a constant'rate of fuel flow through orifice 216 which must also pass through 218. Since the rate of-flow across the fixed orifice 216 is constant, the drop in pressure across 218 will vary substantially inversely as the square of the effective area of the latter orifice as determined primarily by the action of the Pe bellows 225 (compressor discharge pressure modified as a function of temperature) and corrected in response to variations in tailpipe temperature above or below a predetermined value through the motor and its coacting control circuit of Figure 3. The regulator valve 200 functions to establish anabsolute pressure in chamber 205 sufficiently greater than the pressure in chamber 212 to force fuel through the variable area of orifice 213 at a rate determined by the fixed orifice 216 and the constant head thereacross. The metering head across the throttle valve 209 (or feed restrictions 211) is therefore equal to the sum of the constant head across orifice 216 plus the variable head across variable orifice 218. Assuming the afterburning system is turned on and the engine is operating ata speed which will result in the closing of switch 62 of Figure 1, then the tail gate valves 23 and 24 will open and since they are operatively connected to the throttle valve 209, this will result in an increase in the area of the feed restrictions 211, producing an increase in flow of afterburning fuel to the afterburning nozzles.-

As the Po pressure increases, the bellows 225 will be compressed in proportion to such increase as modified by compressor discharge temperature and move the needle 221 in a direction to restrict orifice 218, thereby increasing the metering head across the throttle valve 209 and correspondingly increasing the flow of afterburning fuel; a decrease in PC pressure producing a reverse efiect. Should the temperature in the tailpipe vary above or below a predetermined value as determined by the setting of the bridge circuit 172 of Figure 2 in a manner heretofore described, the area of the orifice 218 will be correspondingly varied. If the temperature rises above such value, the area of the orifice 218 will be increased and reduce the metering head; and if the temperature drops below such value, the area of said orifice will be decreased. This tends to maintain the tailpipe temperature constant under full afterburning operation conditions.

Although only one complete afterburning system plus a modification in the fuel feed control has been illustrated and described, various changes in the form and relative arrangements of the parts may be made to suit require ments.

We claim:

1. For use with a gas turbine engine having a primary burner system, a turbine driven compressor for supplying air under pressure to the burner system and a tailpipe downstream of the turbine terminating in a reaction jet, a thrust augmentation or afterburning system comprising means for conducting afterburning fuel under pressure to the interior of the tailpipe between the turbine and reaction jet, means for regulating the flow of fuel as a function of a pressure generated by the compressor, and means operable as a function of tailpipe temperature for modifying the regulated flow of fuel.

2. For use with a gas turbine engine having a primary burner system, a turbine driven compressor for supplying air under pressure to the burner system and a tailpipe downstream of the turbine terminating in a reaction jet, a thrust augmentation or afterburning system comprising means for conducting afterburning fuel under pressure to the interior of the tailpipe between the turbine and reaction jet, means for metering the afterburning fuel as a function of compressor discharge pressure and .ing afterburning fuel under pressure to the interior of a 1 3 the tailpipe between. the turbine and. reaction jet, means for meteringthe fuel as aftmctiorr ofa pressure generated by the, compressor, means for modifying the quantity of metered fuel as a function of an. engine operating temperature, andmeansfor also modifying the quantity of metered fuel in relation to. the area of the jet, whereby the fuelimeteredsto said tailpipe varies inaccordance with, the afterburning fuelrequirements of said engine.

4. In a gas turbine engine havinga primary burner system, a turbine driven compressor for supplying air under pressure. to theburnersystern and a tailpipe downstream of. the turbine terminating in a reaction jet; an afterburner system comprising, means for varying the effective. area of said. jet, means for actuating said jet area varying means, means for conducting afterburning fuel; under pressure to the interior of the tailpipe between the turbine and reaction jet, means for metering the fuel in response "to. changes in a pressure. generated by, the c ompressor rneans for modifying the metering. action inrelation to. changes in reaction jet area, and means formaintaihingan engine operating, temperature at a predetermined substantially constant value, whereby the fuel, metered to said tailpipe varies in accordance with the afterburning fuel. requirements of said engine.

5. The combination as claimed in claim 4 wherein said, last-Inarnedf means comprises a flow regulating valve adapted, tomodify the-metering actionand which is auto-- maticallyjj positioned by means responsive to variations from a, predetermined afterturbine or tailpipe temperature.

6;. The. combination. as, claimed in claim- 3 whereinmeanshare provided. for modifying. the. compressor generated pressure. as a. function. of a temperature generated bythecompresson In a, thrust. augmentation systenrfor a turbojet enginehaving a. compressor, ataflpipe chamber, a reaction jet and, meansfon varying, the. elfctive area of the jet; mean s for regulating, the, flow of. fuel to said tailpipe chamber. including. a fuehcondfuit having a feed restriction therein, a throttle valve.for, varying the area of said restriction, .a regulator valve. for varying, the. metering head, across saidrestriction, means, responsive: to changes in, a. pressure. generated. by the; compressor for controlling one,ofisaid,valves; means. responsive to.changes in the area, of. thereaction. jet. for. controlling-the other. of said valves, and. means for modifying. the action. of one of said valves asa functionof aftersturbine :or tailpipe temperature whereby the. area. Ofnsaid restriction. and. the meteringhead,thereacross are. controlled to. vary thefuel flow to said tailpipe chamber in accordance with the thrust. augmentation, fuel requirements. of. said engine.

8,111. a. thrust. augmentationsystem. for. a. turbojet engin k having a compressor, a. tailpipe. chamber, a. re action jet and means for varying, the. effective area. of thenjet; awfuel; conduit,- having, a. metering restriction therein, a, throttle .valvefor varying. the. effective area of said. restriction, a regulating, valve: for. varyingthe metering-,head across 1 said restriction, means. responsive to changes in compressordischarge pressure operatively connectedto.saidgthrottle valve, means. responsiveto changes in. the ;area .of said jet.operatively., connectedto said regulating yalve and. means .for modifying, the; action: of one. of. said-valves. as a function :of after-turbine. or. tailpipe temperature wherebyibe; fuel. flow through said .conduit is.,controlled in accordancewitlnoptimum thrust augmentationifuel.requirements ofsaid-engine;

9..r In athrust;augmentationgsystem for a,turbojet. engineglra-vingga,compressor, a tailpipe chamber, a reaction jet and valve means for varyingthea effective area of. thegjet;;a=fuelrconduit .havingametering restriction therein; ,.a. throt tle-valve for; varying the. effectivearea: of the.

restriction;zairegulatinggvalve for controlling :the metering heads acrossisaid-restriction; 1 said valve means: beingoper ativcly;connected.to said throttleivalve, pressureresponsive'imeans connentedzto saidlregulatingvalve; and means for repositioning said pressure responsive means, as a function of a pressure generated by the compressor; whereby fuel may be metered to said tailpipe chamber in accordance with the thrust augmentation requirements of said engine.

10'. A system as claimed in-claim 9 wherein means responsive to changes in after-turbine or tailpipe tentperatu-re above or below a predetermined value is arranged toalso reposition said pressure responsive means.

11.. A system as claimed in claim 9 wherein saidpressure responsive means is operatively connected to a variable bY-Pass bleed or orifice having a needle for varying the efiective area thereof, said needle being con-trolled by means responsive to changes in compressor discharge pressure and also by means responsive to changes in afterturbine or tailpipe temperature.

12. In a thrust augmentation system for a turbojet engine having a tailpipe chamber and a reaction jet; means for metering fuel to said tailpipe chamber, and means operable to automatically render said metering means operative only after the rotational speed of the engine has attained a predetermined value.

13. In a thrust augmentation system fora turbojet engine having a tailpipe chamber, a reaction jet and valve means for varying the effective area of said jet; means for metering fuel to said tailpipe chamber and means r'esponsive to changes in the rotational speed of the engine for initiating the operation of said metering means and said valve means.

14. In a thrust augmentation system for a turbojet engine having a tailpipe chambeiya reaction jet and means for varying the effective area of the jet; means for metering fuel to said tailpipe chamber including a fuel manifold and'a series of discharge nozzles receiving fuel under pressure from said manifold, anda speed sensitive device responsive to changes in the rotational speed of the engine for initiating flow offuel to said manifold and discharge'nozzles and also for producing operation of said area varying means.

15. In an afterburning system for a turbojet engine having a tailpipe chamber, a fuel metering device, a ternperature sensing device for modifying the action of the fuel metering device to maintain a predetermined engine operating temperature by controlling the rate of fuel feed while the afterburning system is in operation; and

means for automatically maintaining a predetermined fixed relationship between said devices having as its modulus a given tailpipechamber temperature when said system is in a nonoperating'" or idle condition.

16; In a system for burning fuel in the tailpipe of: a turbojetengine after the turbine, a fuelzmeteringdevice' having a valve for controlling the rate of fuel new, atemperature responsive device having an element for sensing the temperature in the tailpipe; means connecting said temperature responsive device to said valve to regulate fuel flow in response to changes intailpipe temperature above or below a predetermined value, and means for automatically maintaining said'temperature responsive device and said valve in a predetermined relationship having'as its modulus a given tailpipeternperature when the afterburning system is in non-operating condition.

17. In asystenr for burning fuel in the't'ailpipe of a turbojet engine, fuel metering means havinga valve-for con trolling the rate of fuel flow, and means. for positioning said valve asia function of tailpipe temperature; said latter means including airelectrical valve actuating'device', a thermal responsive element for sensing tailpipe te'mperature, means for' transmitting signals'from said elementto said valve actuating device including an electric circuit having an adjustable bridge therein which is' calibratedto. balance when the-tailpipetemperatureis at a predeter mined value and to become unbalanced when the tempera ture isaboveor below such value, amember movable :tovary. the flow of current through the bridge having. a-=fol-" low-up; connection: with the .motor, said latter member when in a neutral position balancing the bridge, and means for electrically disconnecting the bridge from said element when the system is idle and connecting it to said latter member to automatically spo the valve at a position corresponding to that which it assumes when the thermal responsive element and bridge are electrically connected and in balance.

18. In a thrust augmentation system for a turbojet engine having a compressor, a burner and a tailpipe chamber; means for regulating the flow of fuel to said tailpipe chamber including a fuel conduit having a feed restriction therein, a valve for regulating the flow of fuel through said restriction, a pressure-responsive device operatively connected to said valve, means for subjecting said device to a pressure varying as a function of compressor discharge pressure, and means operable as a function of a temperature which varies with variations in compressor inlet temperature for modifying the pressure to which said device is subjected, whereby the flow of fuel through said restriction to said tailpipe chamber varies as required.

19. A system as claimed in claim 18, wherein air pressure is communicated to said device through a conduit having a variable orifice therein, and the area of said orifice is regulated by a valve which is operatively connected to an element responsive to changes in compressor discharge temperature.

20. In a thrust augmentation system for a turbojet engine having a compressor, a tailpipe chamber, a reaction jet and means for varying the effective area of the jet; means for regulating the flow of fuel to said tailpipe chamber including a fuel conduit having a feed restriction therein, a throttle valve for varying the area of said restriction, a regulator valve for varying the metering head across said restriction, means responsive to changes in temperature varying with changes in compressor inlet temperature for actuating one of said valves, means responsive to changes in the area of the reaction jet for actuating the other of said valves, and means for modifying the action of one of said valves as a function of afterturbine or tailpipe temperature, whereby said regulating means functions to meter fuel to said tailpipe chamber in accordance with the thrust augmentation fuel requirements of said engine.

21. In a thrust augmentation system for a turbo-jet engine having a tailpipe chamber and a reaction jet; means for conducting afterburner starting fuel to said tailpipe chamber, means for igniting the starting fuel flow, and means operable to permit the flow of starting fuel to the tailpipe chamber and to energize said ignition means only after the rotational speed of the engine has attained a predetermined value.

22. In a thrust augmentation system for a turbo-jet engine having a tailpipe chamber and a reaction jet; a pump for pressurizing fuel to said tailpipe chamber, and means operable, to automatically render said pump operative only after the rotational speed of the engine has attained a predetermined value.

23. In a thrust augmentation system for a turbo-jet engine having a tailpipe chamber and a reaction jet; a

temperature sensing device adapted to respond to variations in the temperature in said tailpipe from a predetermined value, and means operable to automatically render said sensing device responsive to the temperature variations only after the rotational speed of the engine has attained a predetermined value.

24. In a thrust augmentation system fora turbo-je engine having a tailpipe chamber and a reaction jet; a temperature sensing device adapted to respond to variations in the temperature in said tailpipe from a predetermined value for producing a signal which varies in magnitude as a function of the degree of variation from said predetermined temperature value, and means operable to automatically render said sensing device responsive to 16 said temperature variations only after the rotational speed of the engine has attained a predetermined value.

25. In a thrust augmentation system for a turbo-jet engine having a tailpipe chamber and a reaction jet; means for metering fuel to sail tailpipe chamber, a temperature sensing device for modifying the action of said metering means to maintain a predetermined engine operating temperature by controlling the rate of fuel feed to said chamber while the thrust augmentation system is in operation, and means operable to automatically render said temperature sensing device operative to maintain said predetermined temperature only after the rotational speed of the engine has attained a predetermined value.

26. In a thrust augmentation system for a turbo-jet engine having a tailpipe. chamber and a reaction jet; means for metering fuel to said tailpipe chamber including a main after burner fuel conduit means, and means operable to permit a flow of fuel through said conduit means to said tailpipe chamber only after the rotational speed of the engine has attained a predetermined value and only after tailpipe chamber temperature has attained a predetermined value.

27. In a thrust augmentation system for a turbo-jet engine having a tailpipe chamber and a reaction jet; .valve means for varying the effective area of said jet, means for actuating said valve means, means responsive to a change in engine speed, and means responsive to a change in tailpipe chamber temperature, said speed and temperature responsive means being operatively connected to said actuating means in such a manner that said valve means is actuable from a relatively closed to a relatively open condition only after engine speed and tailpipe chamber temperature have attained predetermined values.

28. In a thrust augmentation system for a turbo-jet engine having a tailpipe chamber, a reaction jet and valve means for varying the effective area of the jet; means for actuating said valve means, and means operable to automatically render said actuating means operative to open said valve means only after the rotational speed of the engine has attained a predetermined value.

29. In an afterburner system for a turbo-jet engine having a tailpipe chamber, a reaction jet and means for varying the effective area of said jet; means for actuating said valve means, means for metering fuel to said tailpipe chamber operatively connected to and coordinated with said actuating means, and means operable to automati cally render said metering means and said actuating means operative for afterburner operation only after the rotational speed of the engine has attained a'predeter-i mined value. a a

30. A system as claimed in claim 29 wherein means responsive to tailpipe chamber temperature is also adapted to render said metering means and said actuating means operative for afterburner operation.

31. In a thrust augmenting system for a gas turbine engine having a compressor, a tailpipe chamber, and-a reaction jet; a conduit for conducting fuel to said cham her, and fuel control means for controlling the quantity of fuel flowing through said conduit including a fuel metering restriction in said conduit, a metering valve con-- trolling the area of said restriction, an independent fuel pressure differential responsive regulator valve controlling the metering head across said restriction, and-means" responsive to a pressure generated by the compressor and operatively connected to said metering valve for varying the fuel flow through said restriction as a function of said generated pressure, whereby the fuel flow-through said conduit is regulated by the coordinated actionof said metering and regulator valves. 1

32. In a thrust augmenting system for a gas turbineengine having a compressor, a tailpipe chamber, areaction jet andmeans for varying the effective area of the jet; a conduit for conducting fuel to the-tailpipechamber; valve means for controlling the fuel-flow through said conduit, first means responsive to a pressure generated.

by the compressor operatively connected to said valve References Cited in the file of this patent means for controlling the flow of fuel therethrough as a function of said generated pressure, second means re- UNITED STATES PATENTS sponsive to an engine operating temperature operatively 2,095,991 Lysholm Oct. 19, 1937 connected to said valve means for modifying the flow Of 2,374,844 Stokes May 1, 1945 fuel therethrough as a function of said temperature, and 2,378,036 Reggie June 12, 1945 third means for modifying the pressure to which said 2,378,037 Reggio June 12, 1945 pressure responsive means responds. 2,403,398 Reggie July 2, 1946 33. In a fuel control system for a gas turbine engine 2,404,428 Bradbury July 23, 1946 having a combustion chamber and a compressor, a fuel 2,422,808 Stokes June 24, 1947 nozzle for discharging fuel under pressure into Said C m- 2,435,902 Reggio Feb. 10, 1948 bustion chamber, a conduit for conducting fuel to said 2,457,595 Orr Dec. 28, 1948 nozzle, and fuel flow control means in said Conduit in- 2,479,776 Price Aug. 23, 1949 eluding a metering restriction, a metering valve control- 2,514,248 Lombard July 4, 1950 ling the area of said restriction, an independent fuel pres- 2,516,909 Redding et a1 Aug. 1, 1950 sure differential responsive regulator valve controlling the 2,520,434 Robson Aug. 29, 1950 metering head across said restriction, and means are 2,520,967 Schmitt Sept. 5, 1950 sponsive to a pressure generated by the compressor and 2,531,780 Mock Nov. 28, 1950 operatively connected to one of said valves for varying 2,545,856 Orr Mar. 20, 1951 the flow of fuel through said restriction as a function of 2,563,745 Price Aug. 7, 1951 said generated pressure. 2,566,373 Redding a Sept. 4, 1951 34. In a thrust augmentation system for a turbojet 2,580,962 Sdille Ian. 1,1952 engine having a tailpipe chamber, a reaction jet and a 2,623,352 Sdille et al. Dec. 30, 1952 compressor; means for metering fuel to said tailpipe 2,653,446 Price Sept. 29, 1953 chamber, means operable to automatically render said 2,697,909 Chandler Dec. 28, 1954 metering means operative only after the rotational speed 2,700,275 Chandler et a1. Jan. 25, 1955 of the engine has attained a predetermined value, with said metering means including means responsive to the FOREIGN PATENTS discharge pressure of said compressor. 587 558 Gmat Britain May 7 1947 35. In a thrust augmentation system for a turbojet 595357 Great Britain 1947 engine including a tailpipe chamber, a compressor, a re- 41 4 Great Britain 1948 action jet, and valve means for varying the effective area 614202 Great Britain T Dec 1948 of said jet; means for metering fuel to said tailpipe cham- 919OO4 France 1946 her and means responsive to changes in the rotational 934814 France 1948 speed of the engine for initiating the operation of said 941556 France II T Jul}; 1948 metering means and said valve means, with said metering 2503563 gg June 1948 means including a device responsive to a pressure gen erated by said compressor, 

